RloC: A Translation-Disabling tRNase Implicated in Phage Exclusion During Recovery from DNA Damage

Bacteria respond to DNA damage by inducing the expression of numerous proteins involved in DNA repair and the reversible arrests of DNA replication and the cell division cycle (Fernandez De Henestrosa et al, 2000). This general rule may be violated by a conserved bacterial protein termed RloC (Davidov & Kaufmann, 2008). RloC combines structural-functional properties of two unrelated proteins (i) the universal DNA-damageresponsive/DNA-repair protein Rad50/SbcC (Williams et al, 2007) and (ii) the translationdisabling, phage-excluding anticodon nuclease (ACNase) PrrC (Blanga-Kanfi et al, 2006). These seemingly conflicting features may be reconciled in a model where RloC is mobilized as an antiviral back-up function during recovery from DNA damage (Davidov & Kaufmann, 2008), when DNA restriction, the cell's primary immune system is temporarily shut-off (Thoms & Wackernagel, 1984). Another intriguing feature of RloC is its ability to excise its substrate's wobble nucleotide (Davidov & Kaufmann, 2008). This harsh lesion is expected to encumber reversal by phage enzymes that repair the tRNA nicked by PrrC (Amitsur et al, 1987). Evaluating RloC's salient features and purported role requires prior description of its more familiar distant homolog PrrC and a DNA-damage-sensing device RloC shares with Rad50/SbcC. We conclude with an account of cellular RNA and DNA repair tools related to the phage tRNA repair mechanism that counteracts PrrC and may be frustrated by RloC.